linux-kernel - Re: [RFC PATCH v2 4/6] PM: opp: allow control of multiple clocks

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Date:   Tue, 31 May 2022 16:00:29 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Stephen Boyd <sboyd@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Taniya Das <tdas@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [RFC PATCH v2 4/6] PM: opp: allow control of multiple clocks

On 19-05-22, 10:03, Krzysztof Kozlowski wrote:
> Yes, true. The clock frequencies are still changed with each gear, but
> in general the UFS indeed operates on gear concept.

Hi Krzysztof,

I have redesigned the OPP core a bit (two patchsets until now) to make
it easier to add multiple clock support going forward. I need some
inputs from you before moving forward with it now. Will this work for
your use case:

- Add support for multiple clocks, where none of them is primary.

- Which means you won't be able to use dev_pm_opp_set_rate() but will
  need something like dev_pm_opp_set_level(), will add it.

- That is, your OPP table will need to implement levels (I think of
  them as UFS gears) and then call dev_pm_opp_set_level() instead.

- This new API will work just like dev_pm_opp_set_rate(), except that
  it will find the target OPP based on level instead of freq and
  support configuration of multiple clock frequencies.

- Of course both these APIs will share most of the code.

-- 
viresh